Lash adjuster

ABSTRACT

A lash adjuster is provided of which an adjusting screw can be repeatedly fixed in position. 
     The lash adjuster includes a nut member  14  having an internal thread  15  on an inner periphery thereof, an adjusting screw  17  having a external thread  16  on the outer periphery thereof which is in threaded engagement with the internal thread  15,  and a return spring  19  biasing the adjusting screw  17  in the direction to protrude from the nut member  14,  wherein the lash adjuster further includes an initial setting member  25  detachably disposed between the adjusting screw  17  and the nut member  14,  and wherein the adjusting screw  17  is fixed to the nut member  14  due to frictional forces between the initial setting member  25  and the adjusting screw  17  and between the initial setting member  25  and the nut member  14.

TECHNICAL FIELD

This invention relates to a lash adjuster mounted in a valve gear for an engine.

BACKGROUND ART

Valve gears for moving valves provided at engine intake ports or exhaust ports include ones having an arm pivotable about one end thereof and adapted to be pressed down by a cam at its mid-portion, thereby pressing down a valve stem at its other end (swing arm type valve gear), and ones having an arm pivotable its mid-portion and adapted to be pushed up by a cam at one end thereof, thereby pressing down a valve stem at its other end (rocker arm type valve gear).

With these valve gears, due to differences in thermal expansion between component parts of the valve gear while the engine is running, gaps between the component parts of the valve gear tend to change, which could in turn produce noise and compression leakage. When the sliding parts of the valve gear become worn too, the gaps between the component parts of the valve gear tend to change, thus producing noise.

In order to prevent such noise and compression leakage, valve gears ordinarily include a lash adjuster to absorb changes in gaps between component parts of the valve gear.

A typical lash adjuster for use in a swing arm type valve gear comprises a nut member inserted in a receiving hole formed in the top surface of the cylinder head, an adjusting screw having an external thread on its outer periphery which is in threaded engagement with an internal thread formed on the inner periphery of the nut member, and a return spring biasing the adjusting screw in the direction to protrude upwardly from the nut member, thereby pivotally supporting the arm of the valve gear with the adjusting screw (Patent document 1).

A typical lash adjuster for use in a rocker arm type valve gear comprises a nut member inserted in a receiving hole formed in the bottom surface of the arm, which pivots as the cam rotates, an adjusting screw having an external thread on its outer periphery which is in threaded engagement with an internal thread formed on the inner periphery of the nut member, and a return spring biasing the adjusting screw in the direction to protrude downwardly from the nut member, thereby pressing the valve stem of the valve gear (Patent document 2).

With these lash adjusters, when the cam rotates and a load is applied that tends to push in the adjusting screw while the engine is running, the external thread of the adjusting screw is received by the internal thread of the nut member, so that the adjusting screw is axially fixed in position.

With these lash adjusters, when the relative position between the arm and the valve stem changes due e.g. to thermal expansion of the valve gear, the adjusting screw axially moves while rotating in the nut member, thus adjusting gaps between component parts of the valve gear.

When the LASH ADJUSTER is dismounted from the valve gear, the adjusting screw markedly protrudes from the nut member under the biasing force of the return spring. If the lash adjuster is mounted in the valve in this state, the valve can never be seated on the valve seat, which makes complete combustion of the engine impossible. Thus, when mounting the lash adjuster in the valve gear, it is necessary to screw the adjusting screw into the nut member and keep pressing the adjusting screw so as not to protrude from the nut member. It is troublesome to keep pressing the adjusting screw.

In order to avoid this problem, a lash adjuster is proposed in which, in order fix the adjusting screw so as not to protrude from the nut member (initial set position), the adjusting screw is fixed in position by wax contained in the nut member (Patent document 3).

With this lash adjuster, since the adjusting screw is fixed in position by wax, it is not necessary to keep pressing the adjusting screw when mounting the lash adjuster in the valve gear. After the lash adjuster has been mounted in the valve gear, the wax melts due to a rise in temperature while the engine is running, thus releasing the initial set position.

Once the wax melts, it flows out of the nut member. Thus, it is impossible to reuse this wax to fix the adjusting screw in the initial set position again. Thus, it is difficult to remount the lash adjuster after it has been dismounted for overhaul of the engine.

As another means to fix the adjusting screw in the initial set position, it would be feasible to insert a set pin through small-diameter through holes formed in the adjusting screw and the nut member, thereby rotationally fixing the adjusting screw. But in this arrangement, it is necessary to finely adjust the amount by which the adjusting screw is screwed into the nut member, which makes it troublesome to fix the adjusting screw in the initial set position. Also, since the height of the adjusting screw relative to the nut member is fixed, the initial set position is fixed too and is not changeable.

-   Patent document 1: JP Patent Publication 2005-248912A -   Patent document 2: JP Patent Publication 2007-92668A -   Patent document 3: JP Patent Publication 2000-110523A

DISCLOSURE OF THE INVENTION Object of the Invention

An object of the present invention is to provide a lash adjuster of which the lash adjuster can be repeatedly fixed in the initial set position.

Means to Achieve the Object

In order to achieve this object, an initial setting member is detachably disposed between the adjusting screw and the nut member so that the adjusting screw is fixed to the nut member due to frictional forces between the initial setting member and the adjusting screw and between the initial setting member and the nut member. With this arrangement, by attaching and detaching the initial setting member, the adjusting screw can be repeatedly set in the initial set position.

This lash adjuster may have e.g. one of the following structures:

-   1) The adjusting screw has a head protruding from the nut member and     having a larger outer diameter than the inner diameter of the nut     member, and the initial setting member comprises a pair of arm     portions disposed between the head of the adjusting screw and the     nut member, and a operating tab portion connecting together ends of     the respective arm portions, the arm portions being elastically     compressible between the head of the adjusting screw and the nut     member. -   2) A cutout is formed in at least one of the outer periphery of the     adjusting screw and the inner periphery of the nut member that     defines an insertion opening, and the initial setting member is     inserted in the insertion opening in an elastically compressed     state.

With the lash adjuster having the above-described structure 1), when the adjusting screw is screwed into the nut member, thereby compressing the arm portions of the initial setting member between the head of the adjusting screw and the nut member, due to elastic restoring force of the arm portions, frictional forces are produced between the arm portions and the head of the adjusting screw and between the arm portions and the nut member. These frictional forces keep the adjusting screw fixed in the initial set position. By pulling out the initial setting member from between the head of the adjusting screw and the nut member, it is possible to release the initial set position of the adjusting screw.

When the lash adjuster having the above structure 1) is used, the initial setting member may have e.g. one of the following structures:

-   1a) The initial setting member is formed by bending a metal wire,     and the arm portions are formed by bending the metal wire into a     corrugated shape and have elasticity. -   1b) The initial setting member is formed by pressing a metal sheet,     and the arm portions are formed by bending the metal sheet into a     corrugated shape and have elasticity. -   1c) The initial setting member is formed by injection-molding an     elastic resin.

A jig-inserting hole (30) may be formed in the operating tab portion of the initial setting member of the structure 1b) or 1c). With this arrangement, it is possible to pull out the initial setting member by inserting a jig in the jig-inserting hole, thus making it easier to release the initial set position.

With the lash adjuster having the above-described structure 2), when the initial setting member is inserted into an insertion opening defined between the adjusting screw and the nut member in an elastically compressed state, due to elastic restoring force of the initial setting member, frictional forces are produced between the initial setting member and the adjusting screw and between the initial setting member and the nut member. These frictional forces keep the adjusting screw fixed in the initial set position. By pulling out the initial setting member out of the insertion opening, it is possible to release the initial set position of the adjusting screw.

When the lash adjuster having the above-described structure 2) is used, the adjusting screw may comprise a pivot member axially slidably inserted in the nut member, an externally threaded member supporting the end of the pivot member inserted in the nut member and having the external thread on an outer periphery thereof, and an elastic member disposed between the pivot member and the externally threaded member. In this case, the cut-out may be formed on the outer periphery of the pivot member.

When the lash adjuster having the structure 2) is used, the cut-out may be a D-cut portion or comprise two chamfers formed on the outer periphery of the adjusting screw.

If the cut-out is formed so as to separate the external thread on the adjusting screw into a plurality of sections, a plurality of such cut-outs are formed so as be circumferentially equidistantly spaced from each other. With this arrangement, since the external thread and the internal thread axially symmetrically contact each other, the adjusting screw is less likely to incline while the engine is running. Also, if the adjusting screw is formed by forging, forging can be done with higher accuracy.

When the lash adjuster having the structure 2) is used, the initial setting member may further comprise a pull-out portion which can be engaged by a finger, whereby the initial setting member can be pulled out of the insertion opening with the finger. This makes it easier to release the initial set position. The initial setting member is preferably made of rubber or resin because such an initial setting member is lighter in weight than one made of a metal such as iron.

The present invention is applicable e.g. to the following lash adjusters:

-   1) A lash adjuster for use in a swing arm type valve gear wherein     the nut member is inserted in a mounting hole formed in the top     surface of a cylinder head, and wherein the adjusting screw     pivotally supports an arm of the valve gear. -   2) A lash adjuster for use in a rocker arm type valve gear wherein     the nut member is inserted in a mounting hole formed in the bottom     surface of an arm that pivots as a cam rotates, and wherein the     adjusting screw presses a valve stem of the valve gear.

Advantages of the Invention

With the lash adjuster according to the present invention, since the adjusting screw is fixed in position using the detachable initial setting member, the adjusting screw can be repeatedly set in the initial set position.

With the arrangement in which the arm portions of the initial setting member are compressed by the head of the adjusting screw and the nut member, initial setting is complete simply by threading the adjusting screw all the way and it is never necessary to finely adjust the turning amount of the adjusting screw. Thus, initial setting is easy.

With the arrangement in which the initial setting member is inserted in the insertion opening defined between the adjusting screw and the nut member in an elastically compressed state, it is possible to fix the adjusting screw in the initial set position at any desired height by screwing the adjusting screw to the desired height, and then inserting the initial setting member into the insertion opening.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a valve gear including a lash adjuster according to a first embodiment of the present invention.

FIG. 2 is an enlarged sectional view of the lash adjuster shown in FIG. 1, showing the state before the lash adjuster is fixed in an initial set position.

FIG. 3 is an enlarged sectional view taken along line III-III of FIG. 2.

FIG. 4 is an enlarged sectional view taken along line IV-IV of FIG. 2.

FIG. 5 is an enlarged sectional view of the lash adjuster shown in FIG. 2, showing the initial set position of the adjusting screw.

FIG. 6 is a front view of the lash adjuster when the initial set position of the adjusting screw has been released.

FIG. 7 is a enlarged perspective view of a modification of an initial setting member shown in FIGS. 2 to 4.

FIG. 8 shows how the adjusting screw is fixed in the initial set position by the initial setting member shown in FIG. 7.

FIG. 9 is an enlarged perspective view of another modification of the initial setting member shown in FIGS. 2 to 4.

FIG. 10 shows how the adjusting screw is fixed in the initial set position by the initial setting member shown in FIG. 9.

FIG. 11 is a front view of a valve gear including a lash adjuster according to a second embodiment of the present invention.

FIG. 12 is an enlarged sectional view of the lash adjuster of FIG. 11 and its surroundings.

FIG. 13 is a front view of a valve gear including a lash adjuster according to a third embodiment of the present invention.

FIG. 14 is an enlarged sectional view of the lash adjuster shown in FIG. 13.

FIG. 15 is a sectional taken along line XV-XV of FIG. 14.

FIG. 16 is an enlarged sectional view of the lash adjuster showing how an elastic portion of an initial setting member shown in FIG. 14 is inserted in an insertion opening.

FIG. 17 is an enlarged sectional view of the lash adjuster showing the state in which the elastic portion of the initial setting member shown in FIG. 14 has been pulled out of the insertion opening.

FIG. 18 is a perspective view of the initial setting member shown in FIG. 14.

FIG. 19 is a sectional view of a modification of the lash adjuster of FIG. 14.

FIG. 20 is a sectional view taken along line XX-XX of FIG. 19.

FIG. 21 is an enlarged sectional view of the lash adjuster showing the state in which a elastic portion of an initial setting member shown in FIG. 19 has been pulled out of an insertion opening.

FIG. 22 is a front view of a valve gear including a lash adjuster according to a fourth embodiment of the present invention.

FIG. 23 is an enlarged sectional view of the lash adjuster shown in FIG. 22.

FIG. 24 is a sectional view taken along line XXIV-XXIV of FIG. 23.

FIG. 25 is an enlarged sectional view of a lash adjuster according to a fifth embodiment of the present invention.

FIG. 26 is a sectional view taken along line XXVI-XXVI of FIG. 25.

DESCRIPTION OF THE NUMERALS

-   1, 41, 71, 91, 101. Lash adjuster -   2. Cylinder head -   7, 47. Arm -   13, 53. Mounting hole -   14, 54. Nut member -   15. Internal thread -   16. External thread -   17, 57. Adjusting screw -   17A. Pivot member -   17B. Externally threaded member -   17C. Spring washer -   19, 59. Return spring -   23, 63. Head -   25, 28, 32, 75. Initial setting member -   26, 29, 33. Arm portion -   27, 30, 34. Operating tab portion -   31, 35. Jig-inserting hole -   45. Valve stem -   46. Cam -   73, 95, 96. Axial groove -   74, 97. Insertion opening -   77. Pull-out portion -   102. D-cut portion

BEST MODE FOR EMBODYING THE INVENTION

FIG. 1 shows a valve gear including the lash adjuster 1 according to the first embodiment of the present invention. This valve gear includes a valve 4 provided at an intake port 3 of a cylinder head 2 of an engine, a valve stem 5 connected to the valve 4, and a arm 7 pivotable as a cam 6 rotates.

The valve stem 5 extends upwardly from the valve 4 and slidably through the cylinder head 2. An annular spring retainer 8 is fixed to the outer periphery of the valve stem 5 at its upper portion. A valve spring 9 is mounted between the bottom surface of the spring retainer 8 and the top surface of the cylinder head 2. The valve spring 9 biases the valve stem 5 upwardly through the spring retainer 8, thereby seating the valve 4 on a valve seat 10.

The arm 7 has one end thereof pivotally supported by the lash adjuster 1 and the other end kept in contact with the top end of the valve stem 5. At its central portion, the arm 7 carries a roller 11 which is pressed by the cam 6, which is provided over the roller 11. The cam 6 is integrally formed on a camshaft 12 which rotates in unison with the engine crankshaft (not shown).

As shown in FIGS. 1 and 2, the lash adjuster 1 comprises a cylindrical nut member 14 received in a receiving hole 13 formed in the top surface of the cylinder head 2, an adjusting screw 17 having an external thread 16 on its outer periphery at its lower portion which is in threaded engagement with an internal thread 15 formed on the inner periphery of the nut member 14, and a return spring 19 mounted between the adjusting screw 17 and a bottom portion 18 of the nut member 14.

As shown in FIG. 2, the external thread 16 and the internal thread 15 each have a pressure flank 20 that receives pressure when a load is applied that tends to push the adjusting screw 17 into the nut member 14. The pressure flank 20 has a flank angle larger than the clearance flank 21 so that the threads 16 and 15 have a serration-shaped section. When a static axial load is applied to the adjusting screw 17 that tends to push in the adjusting screw, the adjusting screw 17 is prevented from rotating by the frictional resistance between the pressure flanks 20 of the external thread 16 and the internal thread 15. When a static axial load is applied to the adjusting screw 17 that tends to push out the adjusting screw, slip occurs between the clearance flanks 21 of the external thread 16 and the internal thread 15, thus allowing rotation of the adjusting screw 17. By way of example, the pressure flanks 20 of the external thread 16 and the internal thread 15 may have a flank angle of 75°, while their clearance flanks 21 may have a flank angle of 15°.

The return spring 19 is a compression spring and is mounted in the nut member 15 while being axially compressed. The return spring 19 has its bottom end supported on the bottom portion 18 of the nut member 14, and applies, at its top end, an axial force to the adjusting screw 17 through a spring seat 22 that tends to push the adjusting screw 17 out of the nut member 14, thereby biasing the adjusting screw 17 in the direction to protrude upwardly from the nut member 14.

At its portion protruding from the top end surface of the nut member 14, the adjusting screw 17 has a head 23 having an outer diameter larger than the inner diameter of the nut member 14. As shown in 1, the head 23 is engaged in a recess 24 formed in the bottom surface of the art 7 at its end portion, thereby supporting the arm 7. The head 23 has a hemispherical contact surface that is in contact with the recess 24. The arm 7 is pivotable due to sliding between the head 23 and the recess 24.

As shown in FIG. 2, an initial setting member 25 formed by bending a metal wire is inserted between the bottom end surface of the head 23 and the top end surface of the nut member 14. As shown in FIGS. 3 and 4, the initial setting member 25 comprises arm portions 26 diametrically opposed to each other with the adjusting screw 17 disposed therebetween, and an operating tab portion 27 connecting together ends of the respective arm portions 26. As shown in FIG. 5, the arm portions 26 each have a corrugated portion disposed between the bottom end surface of the head 23 and the top end surface of the nut member 14. The corrugated portions are formed by bending the wire in a corrugated shape so as to be axially elastically deformable.

The lash adjustor 1 is assembled into the valve gear e.g. in the following manner.

As shown in FIG. 2, with the arm portions 26 of the initial setting member 25 inserted between the head 23 of the adjusting screw 17 and the nut member 14, the adjusting screw 17 is turned and screwed into the nut member 14 so that the arm portions 26 are compressed by the bottom end surface of the head 23 and the top end surface of the nut member 14. At this time, as shown in FIG. 5, due to elastic restoring force of the arm portions 26, frictional forces are produced between the arm portions 26 and the head 23 of the adjusting screw 17 and between the arm portions 26 and the nut member 14. These frictional forces prevent rotation of the adjusting screw 17, thereby keeping the adjusting screw 17 fixed in position so as not to protrude from the nut member 14 (initial set position).

Next, as shown in FIG. 1, the lash adjuster 1 is inserted into the receiving hole 13 of the cylinder head 2, and the arm 7 and the camshaft 12 are mounted in position. Then as shown in FIG. 6, the initial setting member 25 is pulled out from between the head 23 of the adjusting screw 17 and the nut member 14, thus releasing the initial set position. The adjusting screw 17 thus protrudes while rotating under the biasing force of the return spring 19, thus pushing up the end of the arm 7 until the roller 11 contacts the cam 6.

In this state, when the engine is started, the cam 6 rotates, and the arm 7 is pressed down by a cam lobe 6 a of the cam 6, the valve 4 separates from the valve seat 10, opening the intake port 3. At this time, a load is applied to the adjusting screw 17 that tends to push in the adjusting screw. But since the pressure flank 20 of the external thread 16 is supported by the pressure flank 20 of the internal thread 15, the adjusting screw 17 is axially fixed in position.

As the cam 6 further rotates and the cam lobe 6 a moves past the roller 11, the valve stem 5 rises under the biasing force of the valve spring 9, thereby seating the valve 4 against the valve seat 10, closing the intake port 3.

Strictly speaking, when the arm 7 is pressed down by the cam lobe 6 a of the cam 6, slight slip occurs between the pressure flanks 20 of the external thread 16 and the internal thread 15, thus pushing in the adjusting screw 17. But once the cam lobe 6 a moves past the roller 11 and the load that tends to push in the adjusting screw is removed, the adjusting screw 17 returns to the original position under the load from the return spring 19 which tends to push out the adjusting screw.

While the engine is running, if the distance between the cam 6 and the arm 7 increases due to thermal expansion differences between component parts of the valve gear such as the cylinder head 2, valve stem 5 and arm 7, the adjusting screw 17 protrudes by a larger amount when the cam 6 further rotate after the cam lobe 6 a of the cam 6 presses down the arm 7 until the load is removed, than the amount by which the adjusting screw 17 is pushed in when the arm 7 is pressed down by the cam lobe 6 a of the cam 6. As a result, every time the cam 6 rotates once, the adjusting screw 17 protrudes gradually, thus preventing any gap between the base circle 6 b of the cam 6 and the roller 11.

Conversely, if the contact surfaces of the valve 4 and the valve seat 10 become worn, the biasing force of the valve spring 9 keeps acting on the adjusting screw 17 even while the base circle 6 b of the cam 6 faces the roller 11. Thus, the adjusting screw 17 protrudes by a smaller amount when the cam 6 further rotate after the cam lobe 6 a of the cam 6 presses down the arm 7 until the load is removed, than the amount by which the adjusting screw 17 is pushed in when the arm 7 is pressed down by the cam lobe 6 a of the cam 6. As a result, every time the cam 6 rotates once, the adjusting screw 17 is pushed in gradually, allowing the valve stem 5 to rise. This prevents any gap between the contact surfaces of the valve 4 and the valve seat 10.

When the valve gear is dismounted from the camshaft 12 for overhaul of the engine, the adjusting screw 17 protrudes from the nut member 14 under the biasing force of the return spring 19. In this state, by threading the adjusting screw 17 into the nut member 14 by turning the adjusting screw 17, with the initial setting member inserted between the head 23 of the adjusting screw 17 and the nut member 14, the adjusting screw 17 can be again set in the initial set position.

With this lash adjuster 1, since the adjusting screw 17 can be fixed in position using the detachably inserted initial setting member 25, the adjusting screw 17 can be repeatedly set in the initial set position.

As an alternative way of setting the adjusting screw 17 in the initial set position, it may be feasible to insert a set pin through small-diameter through holes formed in the adjusting screw 17 and the nut member 14. But in this arrangement, it is difficult to align the through hole formed in the adjusting screw 17 with the through hole formed in the nut member 14 by finely adjusting the turning amount of the adjusting screw 17, and thus initial setting is troublesome. In contrast, with the lash adjuster 1, initial setting is complete simply by threading the adjusting screw 17 all the way and it is never necessary to finely adjust the turning amount of the adjusting screw. Thus, initial setting is easy.

With this lash adjuster 1, since it is not necessary to form through holes for inserting a set pin in the adjusting screw 17 and the nut member 14, its manufacturing cost is low.

In this embodiment, the initial setting member to be disposed between the head 23 of the adjusting screw 17 and the nut member 14 is the initial setting member 25 formed by bending a metal wire material. But instead of this initial setting member 25, an initial setting member 28 as shown in FIGS. 7 and 8 may be used, which is formed by pressing a metal sheet material.

As shown in FIGS. 7 and 8, the initial setting member 28 comprises two diametrically opposed arm portions 29, and an operating tab portion 30 connecting together two respective ends of the arm portions 29. The arm portions 29 each have a corrugated portion disposed between the bottom end surface of the head 23 and the top end surface of the nut member 14. The corrugated portions are formed by bending the sheet material in a corrugated shape so as to be axially elastically deformable. The operating tab portion 30 is formed with a vertically extending jig-inserting through hole 31. The initial setting member 28 can be pulled out by inserting a jig (not shown) into the jig-inserting hole 31.

Also, instead of the initial setting member 25, an initial setting member 32 shown in FIGS. 9 and 10 may be used, which is formed by injection-molding an elastic resin. As shown in FIGS. 9 and 10, the initial setting member 32 comprises two diametrically opposed arm portions 33, and an operating tab portion 34 connecting together two respective ends of the arm portions 33. The operating tab portion 34 is formed with a vertically extending jig-inserting through hole 35. The initial setting member 32 can be pulled out by inserting a jig into the jig-inserting hole 35.

FIG. 11 shows a valve gear to which the lash adjuster 41 of the second embodiment according to this invention is mounted. This valve gear includes a valve 44 provided at an intake port 43 of a cylinder head 42 of an engine, a valve stem 45 connected to the valve 44, and an arm 47 that pivots as a cam 46 rotates.

The valve stem 45 extends upwardly from the valve 44. A spring retainer 48 is fixed to the upper portion of the valve stem 45. A valve spring 49 biases the spring retainer 48, thereby seating the valve 44 against a valve seat 50.

The arm 47 has its central portion pivotally supported by a pivot shaft 51, and carries at one end thereof a roller 52 that is in contact with the cam 46. The lash adjuster 41 is mounted to the other end of the arm 47. The cam 46, which is provided under the arm 47, rotates together with the engine crankshaft (not shown), thereby pivoting the arm 47 by pressing the roller 52 with its cam lobe 46 b, which protrudes from its base circle 46 a.

As shown in FIG. 12, the lash adjuster 41 comprises a tubular nut member 54 inserted in a mounting hole 53 formed in the bottom surface of the arm 47, an adjusting screw 57 having an external thread 56 on its outer periphery at its upper portion which is in threaded engagement with an internal thread 55 formed on the inner periphery of the nut member 54, and a return spring 59 mounted between the adjusting screw 57 and the inner bottom surface 58 of the mounting hole 53.

The external thread 56 and the internal thread 55 each have a pressure flank 60 that receives pressure when a load is applied that tends to push the adjusting screw 57 into the nut member 54. The pressure flank 60 has a flank angle larger than the clearance flank 61 so that the threads 56 and 55 have a serration-shaped section. When a static axial load is applied to the adjusting screw 57 that tends to push in the adjusting screw 57, the adjusting screw 57 is prevented from rotating by the frictional resistance between the pressure flanks 60 of the external thread 56 and the internal thread 55. When a static axial load is applied to the adjusting screw 57 that tends to push out the adjusting screw, slip occurs between the clearance flanks 61 of the external thread 56 and the internal thread 55, thus allowing rotation of the adjusting screw 57.

The return spring 59 is a compression coil spring having its top end supported by the inner bottom surface 58 of the mounting hole 53 and applies, at its bottom end, an axial force to the adjusting screw 57 through a spring seat 62 that tends to push the adjusting screw 57 out of the nut member 54, thereby biasing the adjusting screw 57 in the direction to protrude downwardly from the nut member 54.

At its portion protruding from the bottom end surface of the nut member 54, the adjusting screw 57 has a head 63 having an outer diameter larger than the inner diameter of the nut member 54. The head 63 presses the top end of the valve stem 45.

The same initial setting member 25 as used in the first embodiment is inserted between the top end surface of the head 63 and the bottom end surface of the nut member 54. Thus, the initial setting member 25 comprises the diametrically opposed arm portions 26 and the operating tab 27 connecting together two respective ends of the arm portions 26.

With this lash adjuster 41, as in the first embodiment, with the arm portions 26 of the initial setting member 25 inserted between the head 63 of the adjusting screw 57 and the nut member 54, the adjusting screw 57 is turned and screwed into the nut member 54 so that the arm portions 26 are compressed by the bottom end surface of the head 63 and the top end surface of the nut member 54. At this time, due to elastic restoring force of the arm portions 26, frictional forces are produced between the arm portions 26 and the head 63 and between the arm portions 26 and the nut member 54. These frictional forces keep the adjusting screw 57 fixed in the initial set position.

By pulling out the initial setting member 25 from between the head 63 and the nut member 54, it is possible to release the initial set position of the adjusting screw 57. The adjusting screw 57 thus protrudes while rotating under the biasing force of the return spring 59, thus pivoting the arm 47 until the roller 52 contacts the base circle 46 a of the cam 46.

With this lash adjuster 41, since the adjusting screw 57 can be fixed in position using the detachably inserted initial setting member 25, the adjusting screw 57 can be repeatedly set in the initial set position. Since initial setting is complete simply by threading the adjusting screw 57 into the nut member 54, initial setting is easy. Also, since it is not necessary to form through holes for inserting a set pin in the adjusting screw 57 and the nut member 54, its manufacturing cost is low.

With this lash adjuster 41 too, instead of the initial setting member 25, it is possible to use the initial setting member 28, which is formed by pressing a metal sheet material (FIGS. 7 and 8), or the initial setting member 32, which is formed by injection-molding an elastic resin (FIGS. 9 and 10).

FIG. 13 shows the lash adjuster 71 of the third embodiment. Elements corresponding to those of the first embodiment are denoted by identical numerals and their description is omitted.

The adjusting screw 17 has a hemispherical protruding end 72 protruding from the nut member 14. The protruding end 72 is fitted in a recess 24 formed in the bottom surface of the arm 7 and supports the arm 7. The arm 7 pivotable as the protruding end 72 slides in the recess 24.

As shown in FIGS. 14 and 15, an axial groove 73 is formed in the outer periphery of the adjusting screw 17 to extend across the external thread 16 from its top to bottom ends. The axial groove 73 thus separates the external thread 16 into a plurality of sections. The axial groove 73 has a U-shaped section, and defines an insertion opening 74 between the adjusting screw 17 and the nut member 14.

An initial setting member 75 is detachably inserted in the insertion opening 74. The initial setting member 75 comprises an elastic portion 76 inserted in the insertion opening 74, a ring-shaped pull-out portion 77, and a connecting portion 78 connecting the pull-out portion 77 to the elastic portion 76. The initial setting member 75 is integrally formed from resin or rubber.

As shown in FIGS. 16 to 18, the elastic portion 76 is a bifurcated member having arms extending in the direction opposite to the direction in which the elastic portion 76 is inserted. The elastic portion 76 is thus elastically compressed between the inner surface of the axial groove 73 and the pressure flank 20 of the internal thread, thereby producing elastic restoring force, which in turn produces frictional forces between the elastic portion 76 and the adjusting screw 17 and between the elastic portion 76 and the nut member 14. These frictional forces prevent rotation of the adjusting screw 17, thus keeping the adjusting screw 17 from protruding from the nut member 14.

When the initial setting member 75 is inserted into the insertion opening 74, if the free ends of the bifurcated arms of the elastic portion 76 enter the insertion opening 74, they may be caught on the internal thread 15 when the initial setting member 75 is pulled out of the insertion opening 74. Thus, in order to prevent the free ends of the bifurcated arms of the elastic portion 76 from entering the insertion opening 74, the elastic portion 76 has a stopper 79 adapted to abut the top end of the nut member 14 when the elastic portion 76 is inserted into the insertion opening 74.

As shown in FIG. 14, a through hole 80 is formed in the bottom 18 of the nut member 14 that extends vertically through the bottom 18. As shown in FIG. 13, an oil discharge hole 81 is formed in the inner bottom surface of the mounting hole 13 which communicates with the through hole 80. Thus, engine oil flowing into the gap between the external thread 16 and the internal thread 15 from the top end surface of the nut member 14 is discharged through the through hole 80 and then the oil discharge hole 81.

The lash adjuster 71 is mounted to the valve gear e.g. as follows.

As shown in FIG. 14, the adjusting screw 17 is fixed in the initial set position by inserting the initial setting member 75 in the insertion opening 74. Then as shown in FIG. 13, the lash adjuster 71 is inserted into the mounting hole 13, and the arm 7 and the camshaft 12 are mounted in position. In this state, the initial setting member 75 is pulled out of the insertion opening 74 by engaging a finger or a tool with the pull-out portion 77. This releases the initial set position of the adjusting screw 17, and the adjusting screw 17 protrudes from the mounting hole while rotating under the biasing force of the return spring 19, thus pushing up the arm 7 until the roller 11 abuts the cam 6.

With this lash adjuster 71, it is possible to fix the adjusting screw 75 in the initial set position at any desired height by screwing the adjusting screw 17 to the desired height, and then inserting the initial setting member 75 into the insertion opening 74. Thus, if the lash adjuster 71 is used for different kinds of valve lifters, the adjusting screw 17 can be fixed in the initial set position at any desired height according to the kind of the valve lifter used.

With this lash adjuster 71, engine oil flowing into the axial groove 73 from the top end surface of the nut member 14 flows into the gap between the external thread 16 and the internal thread 15, thus lubricating the external thread 16 and the internal thread 15. This makes the external thread 16 and the internal thread 15 less likely to become worn.

With this lash adjuster 71, since the initial setting member 75 is made of resin or rubber, the initial setting member 75 is lighter in weight than a similar initial setting member made of a metal such as iron. The initial setting member 75 is preferably made of resin because it is more easily recyclable.

With this lash adjuster 71, as with the first embodiment, since the adjusting screw 17 is fixed in the initial set position using the detachable initial setting member 75, the adjusting screw 17 can be repeatedly fixed in the initial set position. Also, since the initial setting member 75 can be inserted irrespective of the position of the adjusting screw 17 relative to the mounting hole, it is not necessary to finely adjust the turning amount of the adjusting screw 17. Thus, initial setting is easy.

In this embodiment, the elastic portion 76 of the initial set member 75 is bifurcated. But as shown in FIGS. 19 to 21, the elastic portion 76 may be spherically shaped. In FIGS. 19 to 21, the spherical elastic portion 76 is sized such that it is elastically compressed when inserted into the insertion opening 74.

In FIG. 15, only one axial groove 73 may be formed. But as shown in FIG. 20, a plurality of circumferentially equidistantly spaced axial grooves 73 may be formed. With this arrangement, since the external thread 16 and the internal thread 15 axially symmetrically contact each other, the adjusting screw 17 is less likely to incline while the engine is running. Also, if the adjusting screw 17 is formed by forging, forging can be done with higher accuracy.

In this embodiment, in order to define the insertion opening between the adjusting screw 17 and the nut member 14, the axial groove 73 is formed in the outer periphery of the adjusting screw 17. But such an axial groove may be formed in the inner periphery of the nut member 14 instead of in the outer periphery of the adjusting screw 17. Further alternatively, such axial grooves may be formed both in the outer periphery of the adjusting screw 17 and in the inner periphery of the nut member 14.

In the above embodiment, the cut-out defining the insertion opening 74 is the axial groove 73. But instead. the insertion opening may be defined by a D-cut portion or two chamfers formed on the outer periphery of the adjusting screw 17. The D-cut portion is a cut-out on the outer surface of the adjusting screw 17 extending along a plane parallel to a plane including the axis of the adjusting screw 17. The two chamfers are two flat surfaces formed by cutting out the outer periphery of the adjusting screw 17 so as to extend parallel to a plane including the axis of the adjusting screw 17.

In this embodiment, a compression coil spring is used as the return spring 19 for biasing the adjusting screw 17. But instead of a compression coil spring, a torsion coil spring may be used. In this case, the external thread 16 and the internal thread 15 may be trapezoidal threads or triangular threads.

FIGS. 22 and 24 show the lash adjuster 91 of the fourth embodiment according to this invention. Elements corresponding to those of the second embodiment are denoted by identical numerals and their description is omitted.

The return spring 59 is a torsion coil spring having its top end engaged in a through hole 92 formed in the inner bottom surface of the mounting hole 53 slit and rotationally fixed in position, and its bottom end engaged in an engaging hole 93 formed in the adjusting screw 57, thereby applying torque to the adjusting screw 57 that tends to push the adjusting screw 57 downwardly out of the nut member 54 by its torsional deformation. The adjusting screw 57 is thus biased by this torque in the direction to protrude downwardly from the nut member 54. The protruding portion of the adjusting screw 57 protruding from the nut member 54 is in abutment with the top end of the valve stem 45, thereby pressing the valve stem 45.

The external thread 56 and the internal thread 55 are vertically symmetrical triangular threads. As shown in FIG. 23, an axial groove 95 is formed in the outer periphery of the adjusting screw 57 to extend across the external thread 56 from its top to bottom ends. The axial groove 95 thus separates the external thread 56 into a plurality of sections. Another axial groove 96 is formed in the inner periphery of the nut member 54 to extend across the internal thread 55 from its top to bottom ends, thus separating the internal thread 55 into a plurality of sections. As shown in FIG. 24, the axial groves 95 and 96 have a U-shaped section, and radially align with each other, defining an insertion opening 97 between the adjusting screw 57 and the nut member 54. The same initial setting member 75 as used in the third embodiment is detachably inserted in the insertion opening 97.

As shown in FIGS. 22 and 23, the elastic portion 76 of the initial setting member 75 is elastically compressed between the inner surface of the axial groove 95 and the inner surface of the axial groove 96, thus producing radial elastic restoring force. As a result, frictional forces are produced between the elastic portion 76 and the adjusting screw 57 and between the elastic portion 76 and the nut member 54. These frictional forces keep the adjusting screw 57 in the initial set position.

As shown in FIG. 23, the nut member 54 is open at both ends. Thus, engine oil flowing into the mounting hole 53 through the through hole 92 flows into the gap between the external thread 56 and the internal thread 55, and is discharged through the bottom end of the nut member 54.

The lash adjuster 91 is mounted to the valve gear e.g. as follows.

The adjusting screw 57 is fixed in the initial set position by inserting the initial setting member 75 in the insertion opening 97. Then as shown in FIG. 22, the arm 47 and the cam 46 are mounted to the valve gear. In this state, the initial setting member 75 is pulled out of the insertion opening 97. This releases the initial set position of the adjusting screw 57, and the adjusting screw 57 protrudes from the mounting hole while rotating under the torque of the return spring 59, thus pressing the top end of the valve stem 45.

With this lash adjuster 91, it is possible to fix the adjusting screw 75 in the initial set position at any desired height per pitch of the external thread 56 by screwing the adjusting screw 57 to the desired height until the axial grooves 95 and 96 are radially aligned with each other, and then inserting the initial setting member 75 into the insertion opening 97. Thus, if the lash adjuster 91 is used for different kinds of valve lifters, the adjusting screw 57 can be fixed in the initial set position at any desired height according to the kind of the valve lifter used.

With this lash adjuster 71, engine oil flowing into the axial grooves 95 and 96 flows into the gap between the external thread 56 and the internal thread 55, thus lubricating the external thread 56 and the internal thread 55. This makes the external thread 56 and the internal thread 55 less likely to become worn.

With this lash adjuster 91, since the adjusting screw 57 is fixed in the initial set position using the detachable initial setting member 75, the adjusting screw 57 can be repeatedly fixed in the initial set position.

In this embodiment, the axial grooves 95 and 96 are formed in the outer periphery of the adjusting screw 57 and in the inner periphery of the nut member 54, respectively. But only one of them is sufficient. A plurality of circumferentially equidistantly spaced axial grooves 95 and 96 may be formed. With this arrangement, since the external thread 56 and the internal thread 55 axially symmetrically contact each other, the adjusting screw 57 is less likely to incline while the engine is running.

In this embodiment, as cut-outs for defining the insertion opening 97, the axial grooves 95 and 96, which have a U-shaped section, are formed in the outer periphery of the adjusting screw 57 and the inner periphery of the nut member 54, respectively. But in order to define the insertion opening 97, a D-cut portion or two chamfers may be formed on the outer periphery of the adjusting screw 57. The external thread 56 and the internal thread 55 may be trapezoidal threads.

FIGS. 25 and 26 show the lash adjuster 101 of the fifth embodiment according to this invention. Elements corresponding to those of the fifth embodiment are denoted by identical numerals and their description is omitted.

The adjusting screw 17 comprises a pivot member 17A axially slidably inserted in the nut member 14, an externally threaded member 17B supporting the end of the pivot member 17A inserted in the nut member 14 and having an external thread 16 on its outer periphery, and a spring washer 17C disposed between the pivot member 17A and the externally threaded member 17B. The spring washer 17C may be e.g. a disk spring washer or a wave washer.

A D-cut portion 102 is formed on the outer periphery of the pivot member 17A to extend from its portion protruding from the nut member 14 to its end inserted in the nut member 14. As shown in FIG. 26, the D-cut portion 102 defines an insertion opening 74 between the pivot member 17A and the nut member 14. The return spring 19 applies an axial force to the externally threaded member 17B through a spring seat 22 that tends to push the pivot member 17A out of the nut member 14.

With this lash adjuster 101, as in the third embodiment, it is possible to fix the adjusting screw 17 in the initial set position at any desired height by screwing the adjusting screw 17 to the desired height and inserting the initial setting member 75 into the insertion opening 74 in this state. Also, since the adjusting screw 17 is fixed in the initial set position using the detachable initial setting member 75, the adjusting screw 17 can be repeatedly fixed in the initial set position.

With this lash adjuster 101, engine oil flows from the top end surface of the nut member 14 into the nut member 14 through the D-cut portion 102, thus sufficiently lubricating the external thread 16 and the internal thread 15. This makes the external thread 16 and the internal thread 15 less likely to become worn.

In this embodiment, the cut-out for defining the insertion opening 74 is the D-cut portion 102. But instead of the D-cut portion 102, the insertion opening 74 may be defined by two chamfers or an axial groove. Further alternatively, a cut-out may be formed on the inner periphery of the nut member 14 that extends downwardly from its top end.

In this embodiment, the spring washer 17C is used as an elastic member to be disposed between the pivot member 17A and the externally threaded member 17B. But the spring washer 17C may be replaced by a different elastic member (such as a compression coil spring). 

1. A lash adjuster comprising a nut member (14) having an internal thread (15) on an inner periphery thereof, an adjusting screw (17) having a external thread (16) on an outer periphery thereof which is in threaded engagement with the internal thread (15), and a return spring (19) biasing the adjusting screw (17) in a direction to protrude from the nut member (14), characterized in that the lash adjuster further comprises an initial setting member (25, 75) detachably disposed between the adjusting screw (17) and the nut member (14), wherein the adjusting screw (17) is fixed to the nut member (14) due to frictional forces between the initial setting member (25, 75) and the adjusting screw (17) and between the initial setting member (25, 75) and the nut member (14).
 2. The lash adjuster of claim 1 wherein said adjusting screw (17) has a head (23) protruding from the nut member (14) and having a larger outer diameter than an inner diameter of the nut member (14), and wherein said initial setting member (25) comprises a pair of arm portions (26) disposed between the head (23) of the adjusting screw (17) and the nut member (14), and a operating tab portion (27) connecting together ends of the respective arm portions (26), said arm portions (26) being elastically compressible between the head (23) of the adjusting screw (17) and the nut member (14).
 3. The lash adjuster of claim 2 wherein said initial setting member (25) is formed by bending a metal wire, and wherein said arm portions (26) are formed by bending the metal wire into a corrugated shape and have elasticity.
 4. The lash adjuster of claim 2 wherein said initial setting member (28) is formed by pressing a metal sheet, and wherein said arm portions (29) are formed by bending the metal sheet into a corrugated shape and have elasticity.
 5. The lash adjuster of claim 2 wherein said initial setting member (32) is formed by injection-molding an elastic resin.
 6. The lash adjuster of claim 4 wherein the operating tab portion (30) is formed with a jig-inserting hole (31) for inserting a jig.
 7. The lash adjuster of claim 1 wherein a cutout (73) is formed in at least one of the outer periphery of the adjusting screw (17) and the inner periphery of the nut member (14) that defines an insertion opening (74), and wherein the initial setting member (75) is inserted in the insertion opening (74) in an elastically compressed state.
 8. The lash adjuster of claim 7 wherein the adjusting screw (17) comprises a pivot member (17A) axially slidably inserted in the nut member (14), an externally threaded member (17B) supporting an end of the pivot member (17A) inserted in the nut member (14) and having said external thread (16) on an outer periphery thereof, and an elastic member (17C) disposed between the pivot member (17A) and the externally threaded member (17B), and wherein said cut-out (102) is formed on an outer periphery of the pivot member (17A).
 9. The lash adjuster of claim 7 wherein said cut-out is a D-cut portion (102) formed on the outer periphery of the adjusting screw (57).
 10. The lash adjuster of claim 7 wherein said cut-out comprises two chamfers formed on the outer periphery of the adjusting screw (17).
 11. The lash adjuster of claim 7 wherein there are a plurality of said cut-outs (73), each cut-out (73) separating the external thread (16) on the outer periphery of the adjusting screw (17) into a plurality of sections, and wherein said plurality of cut-outs (73) being circumferentially equidistantly spaced from each other.
 12. The lash adjuster of claim 7 wherein the initial setting member (75) further comprises a pull-out portion (77) which can be engaged by a finger, whereby the initial setting member (75) can be pulled out of the insertion opening (74) with the finger.
 13. The lash adjuster of claim 7 wherein said initial setting member (75) is made of rubber or resin.
 14. The lash adjuster of claim 1 wherein the nut member (14) is inserted in a mounting hole (13) formed in a top surface of a cylinder head (2), and wherein the adjusting screw (17) pivotally supports an arm (7) of a valve gear.
 15. The lash adjuster of claim 1 wherein the nut member (54) is inserted in a mounting hole (53) formed in a bottom surface of an arm (47) that pivots as a cam (46) rotates, and wherein the adjusting screw (57) presses a valve stem of a valve gear.
 16. The lash adjuster of claim 5 wherein the operating tab portion (30) is formed with a jig-inserting hole (31) for inserting a jig.
 17. The lash adjuster of claim 8 wherein said cut-out is a D-cut portion (102) formed on the outer periphery of the adjusting screw (57).
 18. The lash adjuster of claim 8 wherein said cut-out comprises two chamfers formed on the outer periphery of the adjusting screw (17).
 19. The lash adjuster of claim 8 wherein there are a plurality of said cut-outs (73), each cut-out (73) separating the external thread (16) on the outer periphery of the adjusting screw (17) into a plurality of sections, and wherein said plurality of cut-outs (73) being circumferentially equidistantly spaced from each other. 